Writing Formulas and Naming Ionic & Covalent Compounds ©2005 Douglas Gilliland Honors Physical Science @ Sarasota High Sarasota, Florida Chemical Compounds An atom consist of a positively charged nucleus (protons and neutrons) and orbiting electrons. Atoms of elements are not chemically stable until they have 8 electrons (octet rule). Atoms gain, lose or share electrons with other atoms to be come chemically stable ( have 8 valence electrons ). Six valence electrons. Eight valence Not chemically stable. -2 8+ Oxygen Atom electrons. 8+ stable. Oxide Ion Chemically Types of Compounds I o n i c - occurs when a metal loses all its valence electrons to a nonmetal. Metal becomes a cation, nonmetal an anion. C o v a l e n t - two nonmetals share electrons. Neither loses or gains electrons - they share electrons. Neither atom becomes and ion. Ionic Compounds Crystalline Lattice Burning Magnesium 2Mg + O2 → 2MgO 20+ + -2 +2 8+ Magnesium Atom + Oxygen Atom 20+ ➝ + Magnesium Ion + 8+ Oxide Ion Reaction between sodium + chlorine 2Na + Cl2 → 2NaCl 11+ + 17+ Sodium Atom + Chlorine Atom 11+ ➝ + Sodium Ion - + 17+ + Chloride Ion Ionic Compounds Includes a metal and a nonmetal. Metal loses e- and becomes a cation (+). Nonmetal gains e- and becomes an anion(-). Metal comes first followed by nonmetal. Change the name of the nonmetal to -ide. Examples: nitride, sulfide, fluoride, oxide, bromide, iodide, chloride, telluride, phosphide. Valence electrons are electrons in the outer energy level of an atom. Metals have between 1-3 valence electrons. Nonmetals have between 5-7 valence electrons. Lose e- Cations (+ ions) Gain eAnions (- ions) The valence of an elements is the charge it takes when it loses or gains electrons. Metal atoms lose electrons and become + ions (cations) Nonmetals gain electrons and become - ions (anions) +1 +2 Transition Metals Multiple valences +3 -4 -3 -2 -1 0 The 5 Steps for writing an ionic compound formula: Write the symbols of the two elements. Write the valence of each as superscripts. Drop the positive and negative signs. Crisscross the superscripts so they become subscripts. Reduce when possible. Formula for boron oxide 1. Write the symbols of the two elements. B O Formula for boron oxide 2. Write the valence for each element. +3 -2 B O Formula for boron oxide 3. Drop the positive & negative sign. 3 B O 2 Formula for boron oxide 4. Crisscross the superscripts so they become subscripts. 3 B O 2 Formula for boron oxide 4. Crisscross the superscripts so they become subscripts. B O 2 3 Formula for boron oxide 5. Reduce subscripts when possible. (not possible here) B O 2 3 Examples of Reduction Ca 2S 2 → CaS Ge 2 O4 → Ge O2 Be2Te 3 → can’t reduce Al 3 N 3 → AlN Sn 2 O4 → SnO 2 Most Transition elements have 2 valences. Roman numerals are used in the name to show the valence on the ion. 9I :R < Period 4 Transition Metals )X 3T ,K )U 4O )[ @T Examples: Mn Manganese(IV) Mn +4 Fe +2 Iron(II) Fe +3 Cu Copper(I) Cu +1 +6 +2 Manganese(VI) Iron(III) Copper(II) Examples of Transition Metals +2 Iron(II) Fe +3 Iron(III) Fe +1 Copper(I) Cu +2 Copper(II)Cu +2 Manganese(II) Mn +4 Manganese(IV)Mn Naming compounds with a transition metal. formula name Fe2 O 3 Iron(III) oxide ZnCl 2 Zinc(II) chloride AgCl Silver(I) chloride Cu 3 P2 Copper(II) phosphide PbS2 Lead(IV) sulfide MnO2 Manganese(IV) oxide Polyatomic Ions -1 Polyatomic (many atom) ions are covalent molecules with a charge. They behave as if they were a single atom ion. Polyatomic Ions Nitrite -2 SO2 -2 SO3 -2 CO3 Carbonate Nitrate -3 PO4 Phosphate +1 NH4 -1 Ammonium -1 NO2 OH -1 NO3 Hydroxide Sulfite Sulfate Treat polyatomic ions as you would any ion - crisscross to determine the formula. The only difference is that when you have more than one of a specific polyatomic ion in a formula you must encase it in parenthesis. Writing Formulas Cation Anion Ca -1 NO3 Mg +2 -3 PO4 +2 Na +1 +2 Ba OH -1 -2 SO4 Compound Ca(NO3)2 Mg 3(PO4)2 NaOH Ba SO4 As in all ionic compounds you must reduce subscripts, but you cannot change the formula of the polyatomic ion. You can only reduce subscripts outside the parenthesis. Compounds with Polyatomic ions Carbonate -2 CO 3 Sodium carbonate Na 2CO3 Calcium carbonate Ca CO 3 Phosphate Aluminum carbonate Al 2(CO 3)3 -3 PO4 Sodium phosphate Na 3PO4 Calcium phosphate Ca3(PO3 )2 Aluminum phosphate AlPO 3 Covalent Compounds Water Molecule Hydrogen Oxygen Atom Atom Hydrogen Atom Covalent Compounds Two nonmetals share electrons so both have 8 valence electrons. Exception: H Neither takes on a charge - no valence. Must use prefixes in the name. Name tells you the formula. Example: N2O4 is dinitrogen tetraoxide. You cannot reduce the formulas!!! Reaction between hydrogen + oxygen 2H2 + O2 → 2H2O 1+ 1+ + 2 Hydrogen Atoms 8+ Oxygen Atom 1+ 8+ Water Molecule 1+ The Space Shuttle Oxygen Hydrogen Water Vapor Exothermic Reaction 2H2 + O2 → 2H2O Covalent Prefixes Mon - 1 Tetra - 4 Di - 2 Pent - 5 Tri - 3 Hex - 6 A prefix tells you the number of atoms of that element in the compound. Examples of Covalent Compounds N2O3 Carbon tetrahydride CH 4 Phosphorus pentoxide PO 5 disulfur trifluoride S2F3 Dinitrogen trioxide Ionic and Covalent Structure Ionic compounds form a crystalline lattice - a repeating pattern of ions. +3 B ions N-3 ions Boron nitride Water H atoms O atom Covalent compounds form individual molecules that are not connected to each other. Naming Binary Compounds Does the compound have a metal? Yes No Covalent Ionic (Metal cation + Nonmetal anion) Place metal first followed by nonmetal ending in -ide (Two Nonmetals) Contain a Transition Metal? Place the nonmetal furthest to the left on the periodic table first, then No Yes the other nonmetal ending in -ide. Use Roman Do not use Use prefixes to tell the number of Numerals to tell atoms in the compound Roman the valence of mon(o)-1, di-2, tri-3, tetr(a)-4, Numerals the metal. pent(a)-5, hex-6 Examples: Examples: iron(III) oxide copper(II) chloride manganese(IV) oxide silver(I) chloride sodium chloride magnesium nitride aluminum fluoride beryllium oxide Examples: dinitrogen trioxide, nitrogen trichloride, phosphorus pentoxide, sulfur dioxide carbon tetrachloride, dihydrogen oxide Summing up: Ionic Ionic bonding occurs between a metal and a nonmetal. Metals lose all their valence eand become cations. Nonmetals gain enough e- to fill their valence level and become anions. Always crisscross valences and reduce to determine the formulas of ionic compounds Do not use prefixes in the names. Ions form a crystalline lattice. Summing up: Covalent Covalent bonding occurs when two nonmetals share electrons to fill their valence energy level. Never use valence to determine the formula there isn’t any valence. Since the two atoms share electrons, they do not take on a charge. Always use prefixes in the names. Atoms combine to form individual molecules.
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